1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more specifically, it relates to a method of fabricating a semiconductor device including a superposition inspection step for determining properness/improperness of superposed positions of a superposed layer and a resist film employed as a superpositive layer.
2. Description of the Background Art
In a process of fabricating a semiconductor device, a resist film serving as a superpositive layer having a prescribed pattern is provided on a prescribed layer (hereinafter referred to as a superposed layer) for patterning the superposed layer, and employed as a mask for etching the superposed layer or a layer interposed between the superposed layer and the resist film. Therefore, it is important to properly position the resist film with respect to the superposed layer. Thus, it is also important to pattern the resist film itself.
A method of positioning a resist film with respect to a superposed layer 605 is briefly described with reference to FIGS. 12 to 17. FIG. 12 is a plan view schematically showing the structure of a photomask 500 for transferring prescribed patterns to the resist film. The photomask 500 generally comprises wiring pattern regions 501 and 502 provided with wiring patterns for semiconductor devices and a peripheral pattern region 510, enclosing the wiring pattern regions 501 and 502, corresponding to a dicing line of a wafer.
The peripheral pattern region 510 is provided with a superposition mark 530 employed for determining properness/improperness of superposed positions of the superposed layer 605 and the resist film.
Specific purposes of superposition marks are now briefly described. FIG. 13 is a plan view of superposition marks formed on the superposed layer 605 and the resist film respectively, and FIG. 14 is a sectional view taken along the line XIVxe2x80x94XIV in FIG. 13. An etched layer 611 is provided with a superposed layer superposition mark 611H formed to reflect the shapes of holes 605d provided on the superposed layer 605 as superposed layer superposition marks, while the resist film is provided with a resist film superposition mark 701H transferred from the superposition mark 530 of the aforementioned photomask 500.
A plurality of recesses 611h are arranged to form a square thereby defining the overall shape of the superposed layer superposition mark 611H, and the dimension (H) of one side of the square is about 25 xcexcm. When formed, the etched layer 611 partially drops into the holes 605d provided in the superposed layer 605, thereby forming the recesses 611h. The holes 605d are formed through the same step as that of forming contact holes (not shown) in a wiring region of the etched layer 611.
On the etched layer 611, the resist film superposition mark 701H formed on the resist film is provided inside the superposed layer superposition mark 611H. The dimension (h) of one side of the resist film superposition mark 701H is about 10 xcexcm.
A general etching step 800 employing the superposition mark 611H and 701H is now described with reference to FIG. 15. First, a photolithography step is carried out for exposing/etching the resist film (S810). Thereafter a superposition inspection step is carried out with the superposed layer superposition mark 611H and the resist film superposition mark 701H (S820).
In this superposition inspection step (S820), a superposition inspection apparatus (not shown) is employed for reading the positions of the superposed layer superposition mark 611H and the resist film superposition mark 701h from image information of these superposition marks 611H and 701h and determining whether or not the resist film superposition mark 701H is present on a prescribed position (tolerance position) of the superposed layer superposition mark 611H.
If the resist film superposition mark 701H is present on the prescribed position of the superposed layer superposition mark 611H, the superposition marks 611H and 701H are determined as acceptable and the process makes a transition to a development inspection step (S830). If the superposition marks 611H and 701H are rejectable, the resist film is removed so that a new resist film is applied and exposed/etched (S810).
Then, a resist dimension inspection step (S840) and an applied mask confirmation step (S850) are carried out for thereafter executing an etching step for the etched layer 611 through the resist film (S860) and making a transition to a subsequent step (S870).
However, a method of fabricating a semiconductor device including the aforementioned superposition inspection step has the following problems:
In the process of fabricating a semiconductor device, different photomasks may be employed in the same photolithography step due to revision of the semiconductor device pattern, addition of a type-oriented option or the like.
For example, FIG. 16 is a sectional view of a semiconductor device including a first semiconductor layer 601 provided with conductive regions 602, 603 and 604 and an interlayer dielectric film 605 having contact holes 605a, 605b and 605c reaching the conductive regions 602, 603 and 604 respectively.
Contact plugs 607, 608 and 609 reaching the conductive regions 602, 603 and 604 are provided in the contact holes 605a, 605b and 605c respectively. Further, a wiring layer 611A communicating with the contact plug 607 and a wiring layer 611B communicating with the contact plugs 608 and 609 are formed on the interlayer dielectric film 605. The wiring layers 611A and 611B are patterned through a resist film 701A having patterns corresponding to the wiring layers 611A and 611B.
FIG. 17 is a sectional view of another semiconductor device having a basic structure identical to that of the aforementioned semiconductor device shown in FIG. 16. The semiconductor device shown in FIG. 17 is different from that shown in FIG. 16 in a point that the same is provided with wiring layers 611C and 611D communicating with contact plugs 608 and 609 respectively. Therefore, these wiring layers 611C and 611D are patterned through a resist film 701B having patterns corresponding to a wiring layer 611A and the wiring layers 611C and 611D.
Thus, regions X1 to X4 having partially different wiring structures are interspersed as shown in the plan view of FIG. 12, for example, and the difference between the wiring structures is confirmed in the applied mask confirmation step (S850) carried out in the second half of the etching step 800 shown in FIG. 15.
This is because all superposition marks are generally shaped identically to each other and provided on identical positions of peripheral pattern regions of photomasks having different patterns and hence it is impossible to determine whether or not the applied photomask 500 is correct in the steps S820 to S840 shown in FIG. 15. Thus, correctness of the applied photomask 500 is confirmed in the second half of the etching step 800, leading to hindrance of improvement of the working efficiency.
Further, the applied mask confirmation step (S850) is generally manually carried out offline, leading to reduction of the fabrication yield for the semiconductor device resulting from overlook of incorrectness of the photomask 500.
An object of the present invention is to provide a method of fabricating a semiconductor device including a superposition inspection step, capable of efficiently confirming an applied mask and improving the fabrication yield for the semiconductor device.
In order to attain the aforementioned object, the inventive method of fabricating a semiconductor device including a superposition inspection step for determining properness/improperness of a superposed position of a resist film formed on a superposed layer as a superpositive layer with a superposition inspection apparatus comprises the following steps:
A first step is carried out for reading information of a superposed layer superposition mark provided on the aforementioned superposed layer. A second step is carried out for reading information of a resist film superposition mark provided on the aforementioned resist film.
Then, a mark position determination step is carried out for reading the positional relation between the aforementioned superposed layer superposition mark and the aforementioned resist film superposition mark from the aforementioned information of the layer superposition mark and the aforementioned information of the resist film superposition mark, for determining properness/improperness of the position of formation of the aforementioned resist film with respect to the aforementioned superposed layer.
A mark determination step is carried out for comparing the aforementioned information of the resist film superposition mark with information of a registered resist film superposition mark previously registered in the aforementioned superposition inspection apparatus thereby determining whether or not the aforementioned resist film superposition mark coincides with the aforementioned registered resist film superposition mark.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.